In the present study, we aimed to induce precocious intestinal maturation in neonatal rats by the oral administration of polyamines. Groups of 5 rats received either saline, spermidine (10 mumol daily), or spermine (6 mumol daily) orally on the 12th, 13th, and 14th postnatal days. The rats were killed on the 15th postnatal day. After the small bowel was removed, a 1-cm distal ileal segment was removed for histologic examination and the remaining small bowel tissue was homogenized for further biochemical analysis. Polyamine administration was shown to induce structural and biochemical mucosal changes characteristic of postnatal maturation. Lactase, sucrase, and maltase specific activities (micromoles of substrate hydrolyzed per minute per gram of protein) were 80 +/- 10, 10 +/- 3, and 116 +/- 19 for the saline-treated rats; 51 +/- 7, 34 +/- 2, and 315 +/- 37 for the spermidine-treated rats; and 25 +/- 2, 46 +/- 5, and 419 +/- 63 for the spermine-treated rats, respectively. Similar results were obtained with rats, first treated with spermine (6 mumol) on the 7th postnatal day, receiving spermine (6 mumol) daily as described above and killed on the 10th postnatal day. Dose-response experiments performed as reported above in rats whose treatment began on the 12th postnatal day showed that the maturational effects of orally administered spermine are dose-dependent.